[compiz] Compiz session management

[dragoran]

Hello,
After trying to solve a issue with desktop-effects in fedora (compiz 
does not let itself to be replaced by metacity).
We come to the conclusion that the compiz session management code is broken.
When unmanaging the screen compiz should unregister itself from the 
session manager to let a new started wm to take over the screen.
See https://bugzilla.redhat.com/bugzilla/show_bug.cgi?id=229113